EXTERIOR LATEX PAINTING
THE IDEAL TIME TO PAINT
Many times the question arises, "When is the best time to apply latex house paint?" Most paint can labels will say, "Above 50° F." and that's the only limitation. This is really an oversimplification -- however, can you imagine the effect if a paint label read:
"Apply only on properly prepared surface. Conditions should be 60° F. to 85° F., 40% to 60% relative humidity during the time of application and for a period of two weeks thereafter."
The above statement is outrageous, but it does outline ideal painting conditions. To insure a long life house paint job with latex requires common sense and a little cooperation from Mother Nature.
Time of Year: Late Spring or early Fall will afford the best results. Temperatures are mild. One has to watch the threat of rain or high evening humidity. Summer is also a good time to paint, but one should avoid painting when the thermometer goes over the 90° mark.
If at all possible, never use latex during "Indian Summer." Those days in the late fall are the worst time to paint. Any freeze-thaw cycles subjected to a latex paint film during its first two weeks of cure can conceivably shorten the life of the paint job.
In short, the latex house painting season starts after the last frost in the Spring and runs until about two weeks prior to the first expected frost in the Fall.
Time of Day: An early morning start never hurts, but a late finish and you are asking for trouble. Generally one should stop painting a couple of hours before sunset, especially during those days of spring and fall that are cool and humid. Glycol bleeding can result if conditions are just right.
Also, during the day, never paint in direct sunlight. Work opposite the sun.
Temperature/Humidity: Temperatures in the seventies are ideal. Above 85° F. latex tends to dry too quickly and may not properly wet out the surface. When temperatures drop below 60° F. latex curing is retarded, and below 40° F. coalescence is severely hampered. One should not paint if the temperatures may drop to 40° F., even 24 hours after application.
When humidity reaches above 70% the evaporation of water from the latex paint film is suppressed. Avoid painting on those days when humidity is excessively high.
Surface Preparation/Application: Surface preparation is critical when using latex paint. Surface must be free of dirt, mildew and chalk. Apply with a quality applicator to a dry film thickness of 3-4 mils.
Final Thought: One might think they would be better off using oil based paint. WRONG! Using good-painting practices, a latex paint job without a doubt will provide superior durability over an oil based finish.
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